In those times silver was paid by weight, Genesis 43:21 Jeremiah 32:10. Current money with the merchant, i.e. right for quality as well as weight in the judgment of merchants, whose frequent dealing in it makes them more able to judge of it.
Related Commentaries of Genesis 23:16
Genesis 23:16
16 And Abraham hearkened unto Ephron; and Abraham weighed to Ephron the silver, which he had named in the audience of the sons of Heth, four hundred shekels of silver, current money with the merchant.